Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Heat of vaporisation help please

  1. Apr 13, 2010 #1
    Hi, i am writing a assignment about thermal expansion and contraction
    and i would like to know if anyone could explain to me why the heat of vaporisation is nearly seven times that of the heat of fusion for water. I thought it might be hydrogen bonding but this is present in both the liquid and solid phases. any help is appreciated
  2. jcsd
  3. Apr 13, 2010 #2
    To convert ice to water not much energy is needed because there is not much change. Only the bonds or attractive force get weaker but molecules are still close together but in vapor phase molecules gains so much of kinetic energy that they are free to move all around the spaces and so we need to give much more energy.
  4. Apr 13, 2010 #3
    but isnt it the hydrogen bonding that keeps the molecules close together in the first place? I mean, water in its liquid and solid states has hydrogen bonding but not in the gaseous state, so i thought that is why there is so much more energy needed to get it from liquid to gas, to break those bonds
  5. Apr 13, 2010 #4
    yeah, you are correct. Most of the attractive force get ruptured while we get from liquid to gaseous state. Hydrogen bonding is also one among those forces.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook